TONIGHT'S MUST-SEE

"CSI: Crime Scene Investigation," 8 p.m., CBS. Ray Langston (Laurence Fishburne) is a college professor with an unusual seminar. By teleconference, his students talk to Nate Haskell, the convicted "Dick and Jane Killer." Now a "visiting professor" arrives. Actually, it's Gil Grissom (William Petersen), working undercover to face a question: From behind bars, has Haskell been engineering a new round of murders? Now the transition is starting: Petersen leaves (but could return in guest spots); Fishburne steps in. Fishburne, 48, is a first-rate star. He's been big in movies since playing a young soldier in "Apocalypse Now," almost 30 years ago; he has an Oscar nomination and two Emmys, one for acting ("Tribeca") and one for producing ("Miss Evers' Boys"). Still, this show wouldn't have existed without Petersen. CBS people tried to steer him to other shows back in 2000, but he insisted on "CSI." They kept it off their schedule — then inserted it at the last minute. By its second year, "CSI" was No. 2 in the Nielsen ratings; for the next three years, it was No. 1. Spin-offs followed; CBS flourished. Now, midway in his ninth season, Petersen has decided to step down.

TODAY'S MIGHT-SEE

"Planet in Peril: Battle Lines," 4 p.m., CNN. In the modern world, ecology issues aren't always easy or terribly interesting. In Cameroon and the Congo, villagers keep going deeper into the jungle, in search of meat. Scientists worry about animal-borne viruses; many of the hunters, however, carry testing kits with them. In South Africa, sharks become a tourist attraction. Some people argue this makes them more dangerous; others say there's no statistical support for that. Such reports — by Anderson Cooper, Lisa Ling and Dr. Sanjay Gupta — are calm, quiet and complex, but not compelling. One report is more involving: Rwanda — a country in which humans were being slaughtered — has recovered so thoroughly that its mountain gorillas are being preserved.

OF NOTE

"Rudolph's Shiny New Year," 7 p.m., ABC Family. This launches an all-animated night. The best of the bunch is "The Year Without a Santa Claus," at 8 p.m.; it's followed by "Rudolph the Red-Nosed Reindeer and the Island of Misfit Toys" at 9 and " 'Twas the Night Before Christmas" at 10:30.

"Survivor," 7 p.m., CBS. There's one more person to eliminate, before Sunday's finale. Now the hidden immunity idol may come back into play.

"Grey's Anatomy," 8 p.m., ABC. It's an all-rerun night for ABC. In this one, a plumbing leak floods the hospital.

"The Office," 8 p.m., NBC. Christmas parties lose some of their charm, it seems, when someone's hair catches on fire.

"30 Rock," 8:31 p.m., NBC. Parents cause complications during the holidays. Jack tried to ditch his mom (Elaine Stritch, who has already won an Emmy in the role), but failed; Liz was counting on her parents, but they took a cruise instead.

"ER," 9:01 p.m., NBC. As last week's episode ended, Sam (Linda Cardellini) was watching her son hover near death after an accident. Tonight, he's on a ventilator; meanwhile, Morris gets a package from his late father and a woman with a high-risk pregnancy may be deported.